1. Field of the Invention
The subject invention deals with a process for the preparation of fiber composite materials through impregnation of the fibers with solvent-borne polymers followed by evaporation of the solvent, and for a device for the implementation of this process. Such prepregs containing reinforcing fibers and either or both thermoplastic and thermosetting plastic matrix resins are being used in increasing amounts as high performance structural materials.
2. Description of the Related Art
In the preparation of the fiber composite materials or prepregs as they are often called, one advantageously uses a solution of thermoplastic, or, in the case of the thermosetting plastics, a solution of polymer precursors, to impregnate the reinforcing fibers. By this technique, the polymer concentration and the impregnation bath temperature may be varied to achieve optimal viscosity, yielding high quality prepregs.
Removal of the solvent from the impregnated fiber material creates difficulties in this process. Previously, the evaporation of the solvent was carried out thermally. For example, the impregnated solvent-containing reinforcing fibers were led through a heating tower against a counter-current of hot air. In this process, large quantities of air must be circulated in order that the concentration of organic solvent in the escaping air is less than 0.1 percent. Under these conditions, the solvent can only be reclaimed at a very great expense. For practical reasons, the solvent was often burned.
It has been proposed to dry the impregnated reinforcing fibers through exposure to infra red (IR) light. Such irradiation primarily results in heating the air, which in turn causes evaporation of the solvent. In this instance a large and continuous flow of air is required. Furthermore, caution must be taken to ensure that the ratio of air to solvent lies sufficiently far above the explosion limit.